what does it mean when my Volkswagen Passat B8 (2015-2022) shows P0171 code?

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the battery to prevent electrical shorts.
• Allow the engine to cool if it was running.

2. Inspect and Repair Vacuum Leaks

• Tools Required: Vacuum gauge, hose clamps, and replacement hoses.
• Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
• Use a vacuum gauge to check for leaks; repair or replace any damaged hoses.

3. Clean or Replace Mass Air Flow (MAF) Sensor

• Tools Required: MAF cleaner, screwdriver.
• Locate the MAF sensor in the air intake duct.
• Disconnect the electrical connector and remove the sensor.
• Clean the MAF sensor with MAF cleaner; if damaged, replace it with a new unit.

4. Check Fuel Delivery

• Tools Required: Fuel pressure gauge, socket set.
• Connect a fuel pressure gauge to the fuel rail and turn the ignition to the "ON" position (without starting the engine).
• Check the fuel pressure; it should be within the manufacturer’s specifications (typically 50-60 psi).
• If low, inspect the fuel pump and replace the fuel filter if necessary.

5. Inspect Exhaust System

• Tools Required: Visual inspection tools, such as a flashlight.
• Inspect the exhaust system for any visible leaks or restrictions, particularly before and after the catalytic converter.
• Repair or replace any components that are leaking.

6. Test Oxygen Sensors

• Tools Required: Multimeter.
• Locate the upstream and downstream oxygen sensors.
• Disconnect the sensor and connect the multimeter to measure voltage output while the engine is running.
• Replace any faulty oxygen sensors.